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What Happens to a Deck if the Footings are not Deep Enough?

When deck footings are not set deep enough, they become highly susceptible to a process called frost heave. This occurs when moisture in the soil freezes and expands, generating tremendous upward pressure that can have several damaging effects on the structure:

  • Structural Misalignment: The frozen ground exerts enough force to lift shallow footings, which can twist support posts out of alignment and cause the deck frame to warp.
  • Incremental Movement: As the ground repeatedly freezes and thaws, the footing moves upward in small increments. Over time, this shifting can cause fasteners to shear.
  • Safety Risks: The cumulative effect of warping, shearing fasteners, and shifting posts eventually makes the entire deck structure unstable and unsafe.
  • Cracking: Specifically for concrete foundations, this upward pressure is strong enough to crack slabs and footings that are not placed below the frost line.

In Nebraska, building codes typically require a minimum footing depth of 42 inches to reach stable soil temperatures and bypass these destructive freeze-thaw cycles.

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